This study was conducted to investigate the effects of Trichostatin A (TSA) on cumulus expansion during mouse oocyte maturation.COCs were cultured at a density of one COC per ml of medium for 15 h (Ⅰ);TSA (100 nM) was added to the culture medium in the treatment group (Ⅱ);the OOX cumulus cells + FGOs (two FGOs/ml of medium) were cultured in a drop of medium covered with mineral oil for 15h (Ⅲ );TSA (100 nM) was added to the culture medium in the treatment group ( Ⅳ );FGOs and OOX were pretreated with 100 nM TSA for 30 min and were then co-cultured with OOX and FGOs,respectively,for 15 h (V and 15 mg/kg body weight Ⅵ ).